Electrostatic liquid developer system



y 1968 F. HUNSTIGER 3,384,051

ELECTROSTATIC LIQUID DEVELOPER SYSTEM Filed Sept. 21, 1966 INVENTOR.FRANCIS HUNSTIGER M WM 7M? ATTORNEYS United States Patent 0 3,384,051ELECTRDdTATlC LIQUH) DEVELOPER SYSTEM Francis Hunstlger, Parma Heights,Ohio, assignor to Harris-lntertype Corporation, Cleveland, Ohio, :1corporation of Delaware Filed Sept. 21, 1966, Ser. No. 581,064

3 Claims. (Cl, 118637) AESTRACT Gil THE DISCLOSURE A liquidelectrostatic developer includes a drum roll for submerging the imageside of the Web while maintaining the non-image side free of liquiddeveloper in which the drum roll is formed with a blanket ofpolyurethane elastomer which is relatively unaffected by the developerliquid, and a hard squeegee roll engaging the image side of the web,confining slippage to the non-image side of the web.

This invention relates to electrostatic photography and moreparticularly to an improved developer apparatus in which an imagebearing member having an electrostatic image is developed by bringingthe member directly into contact with a liquid developer.

This invention relates primarily to an improved developer system inwhich the electrostatic image bearing member is supported on a drum rollfor movement through a tank containing a liquid developer, and in whicha squeegee roll is applied against the member on the drum roll to removeexcess developer liquid. When such an image bearing member, such as aweb of electrophotographic paper, is pulled through a nip formed betweena hard drum roll surface and a resilient surface on the squeegee roll,there is some slippage at the nip. If this slippage occurs against thenewly developed image, it may cause elongation or smearing of smalldetail such as elongation of dots, fine lines, and the like. While suchelongation may not be readily noticeable, it does have the effect ofreducing the sharpness of the smaller detail and, in systems for makingmultiple-color images, this distortion may be repeated from developerstation to developer sta tion to the point where it could becomeobjectionable, if it is not eliminated at each developer station.

The above disadvantages are eliminated in the developer system of thisinvention by providing the resilient surface on the drum roll andsupporting the image bearing member with its non-image side against theresilient material, The squeegee roll forming the pressure nip may thenpreferably be formed of a suitable hard material.

By placing the resilient material on the drum roll, it is possible toform the squeegee roll with a relatively hard surface which lends itselfto easy cleaning. The back of the image bearing material remains dryagainst the surface of the drum roll. Since the squeegee roll is indirect contact with the image, in the absence of constant cleaning, someghosting or offsetting of the image may occur onto the squeegee roll,which must be removed. Hard squeegee rolls such as made of polishedaluminum, chrome plated, or metal coated with polytetrafluoroethylene,can be easily cleaned and wiped in a continuous operation.

It is important that the resilient material on the drum roll beresistant to the solvent component of the developer liquid. This isparticularly important where the sheet material has a width less thanthat of the drum roll, so that the edges of the roll and the exposedends are wetted by the solvent or thinner, while the portion of the drumroll which is wrapped by the sheet material remains dry. Under suchcircumstances, it is important that no swelling or other dimensionalinstability occur within the resilient material on the drum roll. Ifsuch swelling should occur,

Ce Patented May the web wou d tend to ride toward the high side of theroll and accordingly would become unstable in alignlent, as it wouldtend to move from the center toward either end of the roll after suchswelling occurred.

It is therefore an important object of this invention to provide animproved liquid developer system, as outlined above, in which aresilient material is carried on a drum roll for movement at leastpartially within a developer tank for supporting the movement of imagebearing member through said tank in contact with a liquid developertherein, and in which at least a portion of the drum roll at theresilient covering thereon is in contact with the developer liquid, andin which a further portion thereof supporting the image bearing memberremains dry.

A further object of this invention is the provision of an electrostaticliquid developer system, as outlined above, in which a drum roll ismounted for movement with a portion thereof normally submerged below theliquid surface of a developer tank, and in which a resilient coating isformed on the drum roll of a material having a high resistance toswelling in hydrocarbon liquids.

A still further object of this invention is the provision of anelectrostatic liquid developer system in which a drum roll is positionedwith its periphery at least partially submerged or positioned below theliquid level of a developer tank, an elastomeric surface formed on thedrum roll of material highly resistant to such developer liquid forsupporting the non image bearing side of an image bearing member, and arelatively hard squeegee roll forming a pressure nip with the drum rollwhich is relatively easily wiped or cleaned.

These and other objects and advantages of the present invention will beapparent from the following description, the accompanying drawings andthe appended claims.

In the drawings:

FIG. 1 is a somewhat diagrammatic vertical section of an electrostaticliquid developing apparatus constructed according to this invention;

FIG. 2 is a further vertical section of a developer apparatus which isslightly modified in that the squeegee roll is positioned above theliquid level of the developer tank; and

FIG. 3 is a somewhat diagrammatic end view, with the squeegee rollremoved, showing a typical relationship between the sheet material andthe drum roll in the developer tank.

Referring to the figures of the drawings which illustrate preferredembodiments of the invention, an electrostatic liquid developingapparatus is shown in FIG. 1 as comprising a tank 10 formed with asemi-cylindrical bottom 11, an inlet side 12, and a forwardly andupwardly extending portion 13 at the outlet side 14 thereof. A drum roll15 having a core 16 is rotatably positioned within the semi-cylindricalportion ll of the tank it), with a portion thereof received within thetank 10 and normally submerged below the surface of liquid developer 13carried within the tank i The developer 18 may be formulated accordingto the application of Fauser, Ser. No. 762,756, filed Sept. 23, 19-58,now Pat. No. 3,311,490, and Ser. No. 420,449, filled Dec. 22, 1964, nowabandoned, and generally may consist of charged particles of toner eachof which includes a pigment and resin binder, the toner being suspendedin an electrically insulating carrier liquid and maintained in dispersedcondition throughout the carrier liquid.

The drum roll 15 supports the image bearing member il for movementthrough the developer tank 10 from the inlet side 12 to the outlet side14-. The member 19 has previously been charged and an electrostaticimage formed on its outer or exposed surface. This outer surface issubmerged below the level of the developer liquid 18 as the member movesthrough the tank for development of the electrostatic image. The back orinner surface of the member 19 is maintained dry against the drum rollsince the drum roll 15 is only partially submerged within the developertank and since the degree of wrap exceeds the depth of submersion withinthe tank 10.

The outer covering of the drum roll which is in contact with the sheetmaterial is formed as a layer of elastomeric material 20. The material20 may be formed by casting thereon an elastomer which has goodresilience, toughness, and resistance to abrasion. Particularly, thismaterial must have good resistance to the hydrocarbon carrier liquid ofthe developer 18.

As shown in FIG. 3, the member 19 will frequently have a width which isless than the overall width of the drum roll 15, leaving end portions 23and 24 of the drum roll 15 thereof exposed directly to the developer 18.In addition, the submerged vertical edges of the drum roll 15 aresimilarly exposed. It is important that the elastomeric coating material20 be highly resistant to the solvents in the developer liquid 18 toprevent differential swelling or dimensional instability which wouldotherwise occur at the exposed ends 23 and 24 in relation to therelatively dry center section of the roll.

A suitable material for this purpose has been found to be cast solidpolyurethane elastomer. Such a polyurethane elastomer is a reactionproduct of a polyester and a diisocyanate having a Durometer hardnessfrom 10 on the Shore A scale to 70 on the Shore scale. The preferredrange in accordance with the present invention is between 20 to 50 onthe Shore A scale. A polyurethane elastomer which has been used inaccordance with this invention is a reaction product of a polyesterhaving a Hydroxyl Number of 57-63, an Acid Number of 0.8 to 1.5, aviscosity of between 1000 and 1100 cps. at 73 C. and a specific gravity(ZS/15.5 C.) of 1.19; and a diisocyanate mixture of the 2,4 and 2,6isomers in the ratio of 801296 and 20:2%, respectively. Between 7 andparts by weight of polyester per 100 parts of diisocyanate are useddepending on the hardness required. Typical commercially availablepolyester and diisocyanate materials are available under the trademarkdesignation of Multithrane R 26 and Mondue TD80 of Mobay Chemical Co.

The invention further includes a hard surfaced squeegee roll 25 which ispositioned to form a pressure nip at 26 with the resilient surface orcovering on the roll 15 with the member 19 passing therebetween. Thesqueegee roll is preferably formed with a hard surface and thus my beformed of solid polished aluminum, or chromium or Teflon coated metal,such as steel, or formed of any other hard material which is easilywiped.

The use of a metal squeegee roll 25 is of particular advantage since itpermits the grounding of this roll and the removal of any electrostaticcharges which may tend to otherwise build up on the surface of the roll.

It is important that the squeegee roll 25 be easily wiped or cleanedsince both the rolls 15 and 25 are preferably driven by the member 19,and hard rubbing contact with the squeegee roll 25 should be avoided.For the purpose of cleaning the squeegee roll, a brush, chamois cloth,or wiper 28 may be used as shown in FIG. 1, in which the cleaner 28 ispositioned out of the liquid 18 and engages the surface of the roll 25along its length. Also, to assist in cleaning, the surface of the roll25, or the cleaner 28 may be moistened with thinner, such as showndiagrammatically by the shower head 29 applying a very small quantity ofsubstantially toner-free carrier to the surface of the roll 25.

The embodiment shown in FIG. 2 differs from the embodiment shown in FIG.1 in that the squeegee roll 25 is positioned above the surface of theliquid developer 18. A tray 30 containing clear thinner may be providedjust under the roll 25 and above the tank 10 for constantly wetting thesurface of the roll 25. This provides an arrangement in which thesqueegee nip 26 remains close to the liquid to prevent drying of thesolvent and ink. This arrangement may have some advantage where it isdesired to cause a minimum of agitation of the developer 18. Again, asuitable cleaner 28 is positioned in running engagement with the surfaceof the roll 25 and is moistened by a shower 29 of toner-free carrier orthinner, for removing accumulated particles of toner from the roll 25.

In the operation of the invention, the image bearing member 19 which mayhave a Width less than the width of the drum roll 15, is supported formovement through the developer liquid 18 within the tank 10 supported onthe surface of roll 15 defined by the elastomeric material 20. As themember 19 moves through the pressure nip 26 formed between the hardouter surface of the squeegee roll 25 and the resilient surface of thedrum roll 15 formed by the drum roll covering 20, adhering carrierliquid of the developer is removed from the image side of the member 19.The non-image side is supported on the surface of the drum roll and ismaintained relatively dry. Further, any slippage which occurs in thepressure nip is confined to the non-image side of the member 19 and willaccordingly have no adverse affect upon the quality of the image. Thecleaning apparatus 28 operates constantaly to maintain the hard outersurface of the squeegee roll 25 clean and free of image transfer andoffsetting. Thus, a high quality image may be formed free of distortiondue to slippage at the nip. While the areas 23 and 24 of the covering 20are wetted by the developer, no differential swelling will result whichwould cause instability in the running of a web member through thedeveloper apparatus.

The fact that the apparatus of this invention maintains one side of theimage bearing material essentially dry during development, makes itparticularly useful in systems for perfecting, that is in systems whichprint and develop on each side of a sheet of material. Thus, followingthe electrophotographic forming and developing of an image on one sideof the image bearing material, while maintaining the obverse sideessentially dry as described herein, this side can then be formed withan electrostatic image and developed by the apparatus of this inventionwhile the first side is maintained essentially dry against the drum roll15.

While the form of apparatus herein described constitutes a preferredembodiment of the invention, it is to be understood that this inventionis not limited to this precise form of apparatus and that changes may bemade therein without departing from the scope of the invention which isdefined in the appended claims.

What is claimed is:

1. In an electrostatic liquid developer apparatus in which suspendedtoner particles are carried in an electrically insulating carrier liquidmaking up a developer liquid and applied to a flexible image bearingmember having an electrostatic image on one side thereof for thedevelopment of such image, the improvement for reducing smearing andimproving the image quality, comprising a developer tank adapted tocontain a quantity of liquid developer to a predetermined level, a drumroll at least partially received in said tank with a peripheralsupporting surface thereof in normally submerged relation below saidliquid level and adapted to support and guide such image bearing memberon said surface into and out of said tank with said one side thereofpositioned outwardly of said roll in contact with developer liquid insaid tank while maintaining the opposite side of said image bearingmember essentially free of said developer liquid, said drum rollnormally having a width which exceds the width of said image bearingmember there being a portion of said drum roll surface in contact withsaid developer liquid, the portion of said drum roll surface in contactwith said developer liquid, the portion of said drum roll defining saidouter surface being a blanket of polyurethane elastomer relativelyunaffected by and impervious to said insulating carrier liquid, and arelatively hard squeegee roll forming a pressure nip with said drum rollwith said image bearing member therebetween With said nip thereof beingpositioned above said liquid level for removing excess carrier liquidfrom the developed surface of such image bearing member as it leaves thetank and confining substantially all slippage at said nip with thenon-image side of the image bearing member.

2. The apparatus of claim 1 in which said polyurethane elastomer blankethas a hardness in the range of 20 to 50 on the Shore A scale.

3. The apparatus of claim 1 in which said squeegee roll is positionedabove and out of contact with said developer liquid and furthercomprising a pan positioned beneath said squeegee roll and adapted toreceive carrier liquid free of toner particles with said squeegee rollrunning in contact with said carrier liquid.

References Cited UNITED STATES PATENTS CHARLES A. WILLMUTH, PrimaryExaminer.

PETER FELDMAN, Examiner.

